High-Frequency Audio Bandwidth Extension Using Dual-Density Patches
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Solution Overview
Problem
Existing audio coding methods, particularly at low bit rates, reduce subjective audio quality due to bandwidth limitations, leading to computational inefficiencies and poor approximation of high-frequency bands in audio signals.
Innovation Solution
A method and apparatus that generate a bandwidth extended signal by combining patches with different spectral densities, using harmonic and mixing algorithms to fill gaps in the high-frequency band, ensuring the spectral envelope of the original signal is maintained.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If bandwidth extension is performed using a single patching algorithm, then the approximation of high-frequency bands is simplified, but the spectral density distribution becomes uneven and gaps remain in the high-frequency spectrum
Solution Approach 1:
The patent segments the bandwidth extension process into two distinct patching algorithms: a first patching algorithm that generates a first patch with lower spectral density, and a second patching algorithm that generates a second patch with higher spectral density. This segmentation allows each algorithm to target specific spectral gaps, thereby improving the overall approximation precision of the high-frequency band while maintaining manageable process complexity through modular design.
2Manufacturing precision
If multiple patches with different spectral densities are combined, then the approximation precision of the high-frequency band is improved, but the computational effort increases
Solution Approach 1:
The patent applies local quality by assigning different spectral densities to different patches based on their specific function. The first patch uses lower spectral density for general spectral coverage, while the second patch uses higher spectral density to fill specific gaps and enhance critical frequency regions. This localized optimization improves overall spectral envelope approximation precision without uniformly increasing computational complexity across the entire processing system.
Solution Approach 2:
The patent merges the outputs of two distinct patching algorithms into a single combined patch that represents the high-frequency band. By combining the first patch (lower spectral density) and the second patch (higher spectral density) in a unified structure, the system achieves improved spectral approximation precision while managing computational complexity through integrated processing and shared computational resources.
3Quantity of substance
If the high-frequency band is coarsely characterized with low resolution, then the data rate is reduced, but the subjective audio quality deteriorates
Solution Approach 1:
The patent changes the resolution parameter differentially across frequency bands. The low-frequency band is encoded with high resolution to preserve fundamental audio quality, while the high-frequency band is encoded with lower resolution to reduce data rate. This parameter change is compensated by the dual-patch approach that uses different spectral densities to approximate the high-frequency content, thereby maintaining subjective audio quality despite the reduced resolution in the high-frequency band.
Data Source
AI summary
An apparatus for generating a bandwidth extended signal from an input signal includes a patch generator and a combiner. The input signal is represented for first and second bands by first and second resolution data, respectively, the second resolution being lower than the first. The patch generator generates first and second patches from the first band of the input signal according to first and second patching algorithms, respectively. A spectral density of the second patch generated using the second patching algorithm is higher than a spectral density of a first patch generated using the first patching algorithm. The combiner combines both patches and the first band of the input signal to obtain the bandwidth extended signal. The apparatus scales the input signal according to the first and second patching algorithms or scales the first and second patches, so that the bandwidth extended signal fulfills a spectral envelope criterion.